1. Technical Field
The present invention relates to an ultrasound diagnostic apparatus and a volume data processing method, and more particularly to specification or measurement of an object tissue within a three-dimensional space.
2. Related Art
A three-dimensional space (a three-dimensional data acquisition space) can be formed by scanning a scanning plane, which is formed by scanning an ultrasound beam, in the direction orthogonal to the scanning plane. A Disk Summation method is conventionally known as a method for extracting an object tissue existing within a three-dimensional space and calculating the volume thereof. With this conventional method, each of a plurality of slice data items which are aligned across the object tissue is displayed as a tomographic image, and the outline of the object tissue is manually traced on each tomographic image, enabling the cross sectional area in each slice to be calculated. Then, the cross sectional area and the thickness (an interval between cross sections) for each slice is used to calculate an element volume of each portion (each disc) in the object tissue. By summing these element volumes, a total volume of the object tissue is obtained. According to this conventional method, the volume of the object tissue cannot be obtained with a high precision unless the number of slice data items (i.e. the number of cross sections to be measured) is increased. On the other hand, the burden of a user increases when manual tracing is required with respect to a great number of slice data items. While application of automatic tracing in place of manual tracing with respect to each cross section may be considered, if the outline includes an unclear portion, automatic tracing cannot be performed or the reliability of tracing results is decreased.
JP2004-159997A describes processing for extracting a tissue (cardiac chamber or the like) existing within a three-dimensional space. JP2002-224116A describes extraction of a tissue by using an outline model. JP11-164834A describes technology of correcting a manual tracing result. JP10-305033A, JP2002-330968A, JP2000-107183A, and JP2000-296129 all describe technology of calculating a volume of a tissue.
With regard to specification or measurement of an object tissue, technologies which sufficiently satisfy the demand for achieving a high precision and lessening the burden of a user have not yet been achieved. None of the documents described above describes a combined technology which allows realization of the advantages of both manual tracing and automatic tracing in situations in which the outline of a tissue includes both clear and unclear portions. For example, with regard to the placenta within a uterus during the later weeks of pregnancy, a region of the placenta in contact with the uterus has a small difference in brightness in its ultrasound image whereas a region of the placenta in contact with the amniotic fluid has a significant difference in brightness in its ultrasound image. For the above reasons, there has been a demand for technology which makes it possible to reduce the burden on a user while increasing precision when tracing a placenta in an ultrasound image.